During some well stimulation procedures such as fracturing, an acid is introduced into the wellbore. In order to achieve deep acid penetration, an acid emulsion can be used to retard the reaction rate between the acid and the formation. For example, in an acid-in-diesel emulsion, the retardation of the reaction is due to the diesel external phase which acts as a barrier minimizing the acid transfer to the rock surface. However, at elevated temperatures (i.e., 300° F. and above), the acid-in-diesel emulsion becomes unstable, and thus the retardation mechanism is lost.